I moved into a new home that has a very convoluted HVAC system. Everything appears to function normally with the Honeywell T80XXX thermostat (I forgot to verify the exact model number). What I do need is an upgraded thermostat, one with daily programming and a brain that learns how early it needs to activate to reach temperature by the time needed. I want to stick with a Honeywell, one with the backlit touchpad. I need help choosing the right one & then figuring out the wiring for install. Currently I have the following wires on my existing - G, C, R, W1, Y, W2 & O.Thanks,Regan

Thanks Freon, I was waiting for you to get back online.I've read through that entire document a few times & on page 23, note 4, it states that if I have Y1, W1 & W2 then stop & call a contractor, not explaining the wiring further.Looking at that page I am good with R, O, Y, G & C. I have no L nor E (X or X2). I can put W into Aux, but where do I then put W2

You do not have Y1, only Y (unless you have a 2 stage compressor). That will start the condenser outside. The O will tell the condenser to either cool or heat, depending on how you have the setup program set (0190 in setup). The W1(Aux) is the backup heat (you may have electric heat strips in the air handler or maybe a gas furnace. Be sure you know for the correct setup values)) for when the heat pump, on very cold nights, can not keep up with the thermostat set temperature. W1 is usually dependent on the difference between the house temp and the thermostat set temp. If the house is 2 degrees below the set temp, W1 will activate.Aux (W1) to W1 and W2 to E (W2). Check the setup instructions for having the Emergency (W2) heat operate.

Thanks again Freon.The home has radiant floor heating on its own thermostat, but unfortunately it runs on diesel so its use is not cost effective and it is set at its lowest setting. What I have been able to determine is that the HVAC is a fully indoor heat pump system with, what I am assuming is the backup heat (W2), a hot water valve monitoring a tube & fin heater core situated in the outlet airstream of the HVAC. One of my objectives, probably after the thermostat install (in case I mess it up), is to get a pro in there to explain it all to me. Once I know what is happening I'll be much better off when it comes time to diagnose problems in the future. Regan

Pictures are your friend. Try and draw how your system is configured. You know the air handler, condenser (heat pump outside unit) and thermostat all are interconnected. From your description it seems you have an additional heat exchanger in the ducting for Aux heat. Therefore you have 2 heat exchanger in the supply - one, the evaporator coil, for the heat pump connection and a second for the hot water AUX heat connection. Next try and find the source of the hot water supplied to the heat exchanger in the plenum. Maybe it's an electric hot water heater or an oil fired boiler. The more detailed your pictures (with make and model numbers) the better for any technician and less costly for you.

I'm going to document the system entirely tonight. The supply and return lines for the heater core in the supply plenum go up into the ceiling, which I assume goes out to the garage & to the radiant floor boiler system. I'll verify that too. Can we post pics onto this forum

If you are still following this thread Freon I did some further investigating. I have a Marvair heat pump (VVP57HP A NALW M89 A0) with auxiliary heat coming from a heat exchanger in the outlet plenum being fed by my radiant floor boiler.At the heat pump I have the following hook up for the wires coming from the -R - red wireY - Yellow & white wireO - Orange wireG - Green wireC - Black wireA & W2 are empty - Brown wireThere is then a 2 wire harness that goes to a relay (Radiant Technologies PN 4008) that I assume controls the radiant floor water supply (for my aux heat heat exchanger in the outlet plenum) that has one wire attached to C and another attached to the Brown wire.

At the Thermastat, which I now see is a T8024C those wires are attached as -Red - RYellow - YWhite - W1Orange - OGreen - GBlack - CBrown - W2

You would wire it like the old thermostat with the brown wire going to the Aux terminal in the new thermostat. When you need Aux heat, 24 volts is applied to the Aux terminal then, via the brown wire, that voltage opens the relay/solenoid valve so hot water flows into the heat exchanger. Be sure all power is off when you do the wiring. In the setup programming you will need to know if the heat pump changeover valve is powered for heating or cooling. If you set it incorrectly, you'll feel cold air (AC) when you expect hot air.